1. Field of the Invention.
The present invention relates to automatic replenishment systems for processors of photosensitive material. In particular, the present invention relates to an improved film width and transmittance scanning system for controlling developer and fix replenishment in a graphic arts film processor.
2. Description of the Prior Art.
Graphic arts film processors require replenishment of developer and fix to compensate for changes in the chemical activity resulting from the processing of photosensitive film. Replenishment systems were originally manually operated. The operator would visually inspect the film being processed and would manually operate the replenishment systems as he deemed necessary. The accuracy of these types of manual replenishment systems was obviously based upon the skill of the operator.
In recent years, automatic replenishment systems have found increasing use. These systems typically utilize film transmittance measurements to control the operation of the replenishment system. Examples of automatic replenishment systems are shown in U.S. Pat. No. 4,104,670 to Charnley et al, U.S. Pat. No. 4,057,818 to Gaskell et al, U.S. Pat. No. 4,128,325 to Melander et al and U.S. Pat. No. 4,174,169 to Melander et al. All of these patents are assigned to the same assignee as the present application. Other examples of automatic replenishment systems may be found in U.S. Pat. No. 3,472,143 to Hixon et al, U.S. Pat. No. 3,554,109 to Street et al, U.S. Pat. No. 3,559,555 to Street; U.S. Pat. No. 3,561,344 to Frutiger et al, U.S. Pat. No. 3,696,728 to Hope, U.S. Pat. No. 3,787,689 to Fidelman, U.S. Pat. No. 3,927,417 to Kinoshita et al, U.S. Pat. No. 4,119,952 to Takahashi et al and U.S. Pat. No. 4,134,663 to Laar et al.
In a typical graphic arts automatic replenishment system, a scanner is used to measure transmittance of the film after it has been developed. The scanner includes a light source positioned on one side of the film path, and a light receiver sensing strip positioned on the opposite side of the film path. The amount of light which passes from the light source to the sensing strip is modulated by the film passing inbetween. This is a measurement of transmittance (T), which is the ratio of "transmitted" to "initial" illuminance.
One of the basic types of graphic arts film is half-tone film, which when developed consists of varying sizes of discrete dots. In half-tone film, if a spot is developed at all, it is completely developed, and if a spot is clear, it is completely clear. For example, for a film with "30% dot", thirty percent of the silver has been developed, and this covers thirty percent of the film. With thirty percent of the surface of the film opaque, thirty percent of the incident light will be blocked and seventy percent of the incident light will be detected by the sensing strip. In terms of the definition of transmittance, if the light source prior to film arrival ("no film") is normalized to one hundred percent (100%), and seventy percent (70%) of the light is transmitted, then the ratio of the transmittance to the initial illuminance is seventy percent (i.e. T=70%).
Developer replenishment is based on the amount of silver that was developed and is blocking light. In a half-tone film, developer replenishment is proportional to the percentage dot, that is porportional to one hundred percent minus average percentage transmittance. In the example given above, in which transmittance is seventy percent, thirty percent of the maximum developer replenishment volume recommended for a totally exposed film must be used. The maximum developer replenishment volume recommended for a totally exposed half-tone film is used.
Fix replenishment is often tied directly to developer replenishment, but in fact fix replenishment is inversely related to percentage dot. Accurate fix replenishment requires that the total area of the film and the percentage dot both be known, since the amount of fix which has been exhausted depends upon the clear area of the film after developing.